Although reciprocating internal combustion engines have traditionally incorporated circular cylinder bores, some engine designers have developed oblong and elliptical cross section cylinders. In general, noncircular cylinder bores offer advantages in terms of both smaller engine package volume as well as a potential for increasing intake and exhaust port area as compared with conventional circular cylinders. Of course, improved flow through cylinder ports may be translated into increased engine efficiency and power output. Unfortunately, the fabrication and assembly of components for noncircular cylinder engines has been difficult because special machining operations have been required for maintaining accuracy in the fabrication of the complex curves presented by the cylinder bores.
The present invention provides a noncircular piston bore having pistons and bores which employ simple circular design elements. An engine having a configuration according to the present invention may be produced with conventional boring and honing equipment. And, piston rings used with the present engine need not be of the more expensive spring loaded type used with conventional noncircular cylinder engines.
The present engine architecture offers an additional advantage for lean burn engines. When employing lean burn, a smaller combustion chamber is advantageous. Smaller combustion chambers promote high turbulence, mixed flow, and uniform small-to-moderate eddy flow structures, which all support good combustion. The present invention allows smaller combustion chambers to be used with a larger cylinder displacement.